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Re: [Amps] SCR to adjust 240v to 200v

To: Michael Clarson <>
Subject: Re: [Amps] SCR to adjust 240v to 200v
From: Jim Durham <>
Date: Fri, 12 Aug 2016 17:11:05 -0400
List-post: <">>
My real reason for asking was not whether the SCR would work to vary the voltage, that's done all the time, but it does put spikes in the AC waveform. I'm sure Henry never anticipated such and how the choke and filter cap in the power supply would love that (or not).


73 de Jim W2XO

On 08/12/2016 03:41 PM, Michael Clarson wrote:
Jim: Motorola did something like you describe in their "MOTRAC" series base stations (beige cabinets) in the 1960s and 70s. These were 250-350 watt output stations using a pair of 8560s as finals. They regulated B+ with SCRs in the transformer primary. All done at 60 Hz and never had any RFI issues from these supplies. I do not have any manuals. Later versions of these stations used constant voltage transformers. Good luck finding a solution. --73, Mike, wv2zow

On Fri, Aug 12, 2016 at 1:07 PM, Jim Durham < <>> wrote:

    Hello all,

    This is my first posting, so Howdy..

    I have a Henry 2k-2 (modified to take 3-500Zs).  After I bought
    it, some years back, I fired it up and tube filaments were very
    bright and HV was high.

    Talked to Henry. They asked me the plate transformer number, which
    they looked up and said "Oh, that's the 200v European
    transformer". So, I put a hefty variac on the 240v AC incoming and
    all is fine, except I'd like to ditch the variac and was wondering
    about if anyone on here had any wise words about using an SCR
    instead to back the AC voltage off.

    My experience with big SCRs (TV studio lighting) was that they
    tend to  put out a lot of RF hash.  I also wonder about how the
    choke and filter cap in the power supply would like non-sinusoidal
    AC waveform?

    Anyone have any experience with this?

    Thanks and 73,

    Jim, W2XO

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